Ajax_Controller.php

<?php
/**
 * Ajax_Controller extends CI_Controller and accepts only xmlhttprequest (AJAX) requests.
 * Directly requesting this controller (or one extending this class i.e. https://example.com/some_class/some_method) 
 * or a request including a method, i.e. https://example.com/groups_admin/groups_list, 
 * will produce the standard CodeIgniter "404 Page Not Found" screen. 
 * 
 * The methods of this class provide convenient gathering of inputs (with optional checking for required inputs), 
 * outputting the appropriately encoded response, or outputting an error response.
 *
 * @author dave friend
 */
defined('BASEPATH') OR exit('No direct script access allowed');

class Ajax_Controller extends CI_Controller
{

    protected $requestMethod;

    public function __construct()
    {
        parent:: __construct();

        if(FALSE === $this->input->is_ajax_request())
        {
            log_message('error', "Attempted non-xmlhttprequest to ".$this->router->class."::".$this->router->method);
            show_404('', FALSE);
        }
        $this->requestMethod = $this->input->method();
    }

    /**
     * Captures either the $_POST or $_GET array and optionally checks for existence of certain keys. 
     * 
     * @param mixed $input_keys Can be a field name (string) or an array of field name strings. 
     * Arrays should be simple lists i.e. ['id', 'year']
     * $input_keys (if any) must be in the desired input array. 
     * If any $input_keys are missing an error response is output ending the script.
     * 
     * @param string $requestMethod Determines which "super global" ($_POST or $_GET) is captured. 
     * Valid values are 'auto' (default), 'get' or 'post'. The default will base the capture on the server request
     * method returned by CI_Input::method(). An invalid $requestMethod value results in 'auto' being used.
     * 
     * @return mixed Returns the input array ($_GET or $_POST) determined by $this->requestMethod. 
     * Returns NULL if the input array is empty and $input_keys is FALSE.
     * If $input_keys is provided and any key is missing from the requested array an AJAX error is triggered.
     * The AJAX error ends script execution.
     */
    public function getInputs($input_keys = FALSE, $requestMethod = 'auto')
    {
        $requestOptions = ['auto', 'get', 'post'];
        if(!is_string($requestMethod) || FALSE === in_array($requestMethod, $requestOptions))
        {
            $this->ajax_error(); // Huh!?! Report internal server error
        }

        if($requestMethod !== 'auto')
        {
            $this->requestMethod = $requestMethod;
        }

        $inputs = $this->input->{$this->requestMethod}();

        if($input_keys)
        {
            if(empty($inputs))
            {
                $inputs = FALSE;
            }
            else
            {
                $input_keys = is_array($input_keys) ? $input_keys : [$input_keys]; //need an array
                foreach($input_keys as $key)
                {
                    //if the key is not in requested array then mark $inputs as FALSE
                    if(!array_key_exists($key, $inputs))
                    {
                        $inputs = FALSE;
                        break;
                    }
                }
            }

            if(!$inputs)
            {
                //Produce an AJAX error ending script execution
                $this->ajax_error("Bad Request", '400');
            }
        }
        return $inputs;
    }

    /**
     * Output a response
     *
     * @param mixed $data The data to output. It will be encoded according to $output_type.
     * @param string $output_type The output encode type. 
     *    Options 'json', 'xml', 'html', or 'text'. Defaults to 'json'.
     */
    public function response($data = NULL, $output_type = 'json')
    {
        // Encode data and set headers
        switch($output_type)
        {
            case 'json':
            default:
                $content_type = 'Content-Type: application/json';
                $out = json_encode($data);
                break;

            case 'html':
                $content_type = 'Content-Type: text/html';
                $out = $data;
                break;

            case 'text':
                $content_type = 'Content-Type: text/plain';
                $out = $data;
                break;

            case 'xml':
                $content_type = 'Content-Type: application/xhtml+xml';
                $out = $this->array_to_xml($data);
                break;
        }

        $this->output
            ->set_status_header('200')
            ->set_header($content_type)
            ->set_header('Cache-Control: no-store, no-cache, must-revalidate')
            ->set_header('Pragma: no-cache')
            ->set_header('Access-Control-Allow-Origin: '.$this->config->base_url())
            ->set_header('Content-Length: '.strlen($out))
            ->set_output($out);
    }

    /**
     * Output an error response with a message
     *
     * @param string $msg The reason string in the response header, default= "Internal Server Error"
     * @param string $status Header status code, default '500' which is appropriate for an "Internal Server Error"
     * @return void  Does not return. Instead, after outputting the error it calls exit() ending script execution.
     */
    public function ajax_error($msg = "Internal Server Error", $status = '500')
    {
        $this->output
            ->set_status_header($status)
            ->set_header("Content-Type: text/plain")
            ->set_output($msg)
            ->_display();
        exit;
    }

    /**
     * Convert an array to an XML string. Must be an associative array, eg. ('my_data' => 'something', 'data' => '1/1/1970')
     *
     * @param array $array The array to be converted to an XML string.
     * @param integer $level The XML version. Default 1.0
     * @return string
     */
    protected function array_to_xml($array, $level = 1)
    {
        $xml = '';
        if($level == 1)
        {
            $xml .= '<?xml version="1.0" encoding="ISO-8859-1"?>'."\n<array>\n";
        }
        foreach($array as $key => $value)
        {
            $key = strtolower($key);
            if(is_array($value))
            {
                $multi_tags = false;
                foreach($value as $key2 => $value2)
                {
                    if(is_array($value2))
                    {
                        $xml .= str_repeat("\t", $level)."<$key>\n";
                        $xml .= array_to_xml($value2, $level + 1);
                        $xml .= str_repeat("\t", $level)."</$key>\n";
                        $multi_tags = true;
                    }
                    else
                    {
                        if(trim($value2) != '')
                        {
                            if(htmlspecialchars($value2) != $value2)
                            {
                                $xml .= str_repeat("\t", $level)."<$key><![CDATA[$value2]]>"."</$key>\n";
                            }
                            else
                            {
                                $xml .= str_repeat("\t", $level)."<$key>$value2</$key>\n";
                            }
                        }
                        $multi_tags = true;
                    }
                }
                if(!$multi_tags and count($value) > 0)
                {
                    $xml .= str_repeat("\t", $level)."<$key>\n";
                    $xml .= array_to_xml($value, $level + 1);
                    $xml .= str_repeat("\t", $level)."</$key>\n";
                }
            }
            else
            {
                if(trim($value) != '')
                {
                    if(htmlspecialchars($value) != $value)
                    {
                        $xml .= str_repeat("\t", $level)."<$key>"."<![CDATA[$value]]></$key>\n";
                    }
                    else
                    {
                        $xml .= str_repeat("\t", $level)."<$key>$value</$key>\n";
                    }
                }
            }
        }
        if($level == 1)
        {
            $xml .= "</array>\n";
        }
        return $xml;
    }
}